Electrodeposition of coating layers on subtrate structures

ABSTRACT

A CURRENT IS PASSED THROUGH A CATHODE AND AN ARTICLE ADAPTED TO FUNCTION AS AN ANODE, THE CATHODE AND ANODE BEING DISPOSED IN AN ELECTROLYTIC VESSEL CONTAINING AN EMULSION PREPARED BY DISPERSING FINE PARTICLES OF A FILLER IN AN AQUEOUS SOLUTION HAVING AS ITS PRINCIPAL CONSTITUENT AN ANIONIC, POLYVALENT POLYELECTROLYTE CONSISTING OF A RESIN COMPONENT, WHEREBY A MIXTURE OF THE FINE PARTICLES AND RESIN COMPONENT IS ELECTRODEPOSITED ON THE ARTICLE. THE COATING LAYER IS THEN DRIED TO CAUSE POLYCONDENSATION OF THE RESIN COMPONENT TO FORM A FILM WHICH FUNCTIONS DIRECTLY AS A BINDER BETWEEN THE FINE PARTICLES.

March 1972 AKIRA MATSUSHITA 3,647,651

ELECTRODEPOSITION OF COATING LAYERS ON SUBSTRATE STRUCTURES Filed Dec.18, 1968 FIG. I(B) FIG. I(A) United States Patent O 3,647,661ELECTRODEPOSITION OF COATING LAYERS ON SUBTRATE STRUCTURES AkiraMatsushita, 99, 2-chome, Kosugigoten-cho, Kawasaki-shi, Japan Filed Dec.18, 1968, Ser. No. 784,552 Claims priority, applizcatioiilgpan, Dec. 23,1967,

Int. Cl. B01k 5/00; C23b 13/00 US. Cl. 204-181 12 Claims ABSTRACT OF THEDISCLOSURE BACKGROUND OF THE INVENTION This invention relates generallyto the field of electrodeposition of materials and more particularly toimprovements in techniques for causing electrodeposition on any selectedsubstrate or base structure of at least one coating layer containing anadditive capable of affecting electromagnetic, dielectric, optical,and/or mechanical properties of substances.

Heretofore, various methods such as painting, evaporation deposition,and electrodeposition by such techniques as electroplating have beenknown as techniques for causing coating layers as mentioned above to bedeposited on and adhere to substrate structures. By these conventionalmethods, however, it has been extremely difiicult, it not impossible, inmany cases to deposit truly uniform and fine-texture coating layers onsubstrate structures in a simple manner. Some of the reasons for thisdifiiculty are set forth below.

Among the numerous articles requiring coating layers, there are variouskinds of magnetic recording mediums or materials, which are produced byvarious respective methods. For example, the process in the productionof magnetic tapes used in magnetic sound recording and imagetranscription or video recording includes the steps of admixing amagnetic oxide such as 'y-Fe O or Fe O in powder form with a resinsolvent to prepare a mixture of the consistency and form of paint andapplying this mixture as uniformly as possible as a thin layer on thesurface of a substrate or carrier structure in sheet form or tape formmade of a material such as Mylar (a polyethylene terephthalate resinproduced by E. I du Pont de Nemours & Co., Inc., U.S.A.) and celluloseacetate.

Sound recording wires are made by wire drawing magnetic alloys ofmagnetic substances such as iron, nickel, and cobalt or coating thesurface of a non-magnetic wire with a thin film or magnetic alloy by amethod such as electroplating, evaporation deposition, sputtering, orcladding.

In the memory devices such as magnetic drums and magnetic disks used inelectronic computers, their magnetic recording mediums are alsofabricated by methods similar in principle to the above mentionedconventional methods.

In the production of a magnetic recording medium by applying as acoating a known magnetic material ren- 'ice dered into a paint state asmentioned above, it is necessary, in order to increase the remanence(residual magnetism) by increasing of the degree of filling of themagnetic material, to use magnetic powder which has been rendered intoextremely fine particles when preparing the magnetic paint and to carryout thorough mixing so as to obtain good dispersion of the powder in thebinder resin and uniform surface finish. Moreover, the paint applicationalso necessitates a complicated process requiring great care uch asspraying, use of a whirler, or electrostatic coating.

Even when such care is exercised in the preparation and application ofthe magnetic paint, evaporation of the organic solvent andgelatinisation of the binder resin tend to occur during paintapplication step or the heating and drying step and give rise to athickness reduction phenomenon. As a result, uniform dispersivity of themagnetic material, fineness of the magnetic material, and uniformity ofthe finished thickness are impaired.

Consequently, there is a lack of uniformity of the internal magneticfield within the magnetic layer at the time of recording, and impairmentof high-density recording such as causing of nonuniformity ofdemagnetisation occurs. For this reason, it has been the common practicein the production of the magnetic materials to carry out severalrepeated cycles of the paint application step and the drying step withthe aim of attaining the above men tioned uniformity.

Furthermore, in the case of known magnetic recording mediums coated witha ferromagnetic alloy film as mentioned above, when this film is madethin so that it has a thickness of the order of a number of microns orsome thousands of angstroms with the aim of preventing eddy currents anddemagnetising fields and of increasing the unit of magnetisation withina unit volume, the formation of such a magnetic alloy film in a uniformmanner is accompanied by various technical difficulties in actualpractice. Moreover, since the magnetic coating is a thin film, severalproblems such as those relating to the adhesivity with respect to thesubstrate, the mechanical strength, and wear resistance of the filmstill remain to be solved.

SUMMARY OF THE INVENTION It is an object of the present invention toovercome the above described difficulties and provide a method ofelectrodepositing on substrates coating layers of greater uniformity andfiner texture than those which can be deposited by known methods.

Another object of the invention is to provide a method of the abovestated character which can be practiced by an extremely simple and rapidprocess by means of relatively simple apparatus.

The foregoing objects and other objects and advantages as will presentlybecome apparent have been achieved by the present invention which,briefly summarised, provides a method for electrodepositing layers onsubstrate structures which is characterised by the steps of preparing anemulsion electrolyte by dispersing fine powder particles of a coatingmaterial (filler) in an aqueous solution having an anionic, polyvalentpolyelectrolyte consisting of a resin component as its principalconstituent, adapting a substrate structure to function as the anode inthe emulsion electrolyte, applying an electrical potential across theanode and cathode thereby to cause the resulting mixture of coatingmaterial particles and high-polymer resin to be electrodeposited on thesubstrate structure, and drying the coating layer thus electrodepositedthereby to cause polycondensation of the coating high-polymer resin, theresin component thereof providing a film to function as a binder betweenthe fine particles of the coating layer.

3 While, in the practice of the invention, the use of direct current asthe process current produces amply satisfactory results, it is possibleto carry out particularly effective.

electrodeposition through the use of a combined current consisting of adirect current and a current varying with time, such as alternatingcurrent, pulse current, highfrequency current, and pulses, superimposedon the direct current for reasons and in the manner as describedhereinafter in detail with respect to electrodeposition of magneticrecording material.

The nature, principle, utility, and details of the invention will becomemore clearly apparent from the following detailed description, beginningwith general considerations and concluding with specific examples ofpreferred embodiment of the invention, when read in conjunction with theaccompanying drawing, in which like parts are designated by likereference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1(A) is a schematic diagram illustrating one example of anelectrical circuit for the practice of the invention;

FIGS. 1(B) and 1(0) are schematic diagrams respectively showing examplesof modifications of the circuit shown in FIG. 1(A);

FIGS. 2 and 3 are fragmentary perspective views, with parts cut away,respectively showing two examples of magnetic recording mediums in wireor rod form fabricated in accordance with'the method of the invention;and

FIGS. 4 and 5 are fragmentary perspective views, with parts cut away,respectively showing two examples of magnetic mediums in sheet or tapeform fabricated in accordance with the method of the invention.

DETAILED DESCRIPTION As a representative application of the presentinvention, one aspect thereof, that is, electrodeposition of magneticlayers of magnetic recording mediums on the substrates thereof is setforth in the following detailed description beginning with generalconsiderations and concluding with specific examples of preferredembodiment of the invention.

The aforedescribed difiiculties encountered in the prior art can beovercome by the present invention providing, in one aspect thereof, amethod which comprises preparing an emulsion by dispersing fineparticles of a magnetic powder in an aqueous solution having an anionicpolyvalent polyelectrolyte consisting of a resin component as itsprincipal constituent, placing the substrate structure to be coated byelectrodeposition as an anode in this emulsion, impressing a D-C voltagebetween the anode and the cathode thereby to electrodeposit on thesubstrate structure an electrically insulative mixture of the finemagnetic particles and the resin component, water washing the coatingthus electrodeposited, subjecting the same to a drying process to causethe deposited resin component undergo polycondensation andsolidification, and causing the resin component thereof to form directlya film as a binder between the fine magnetic particles.

In this manner, a magnetic electrodeposited layer of high uniformity andfine texture can be produced, whereby a magnetic recording medium havinghighly desirable characteristics can be obtained.

The above described method can be improved by superimposing a current toany desired magnitude which varies with time, such as an alternatingcurrent, a pulsating current, high-frequency current, or pulses, inaddition to the electrophoretic energy of the anions toward the anodedepending on the D-C potential gradient during the electrical powerapplication for electrodeposition and carrying out theelectrode-position while a component force for deflecting theelectrophoretic direction of the anions or retarding the velocitythereof is applied. By this improved method, the process of depositing auniform coating can be accomplished with further effectiveness.

By the method of the invention as described above for electrode-positionof recording magnetic material, the resin component in the depositedcoating can be polycondensed and solidified by merely drying theelectrolytic emulsion after electrodeposition thereof on the substrate,and the resin component thereof directly undergoes complete gelation toform a solid film as a binder between the fine magnetic particles.

Accordingly, by introducing the coated substrate structure directly intoa heat treatment vessel and drying the same or by pressing a heating jigwith a mirror surface against the electrodeposited surface to cause itto form a solid film, it is possible to obtain in a very simple manner asmooth surface having uniform dispersivity and fineness of the magneticmaterial without carrying out, thereafter, surface finishing by aprocedure such as lapping.

Furthermore, in the case wherein, for the electrodeposition current, abias current which varies with time is superimposed on a direct current,the electrophoretic effect during electrodeposition is promoted, and theeffectiveness in discharging and separating of substances such ascations, moisture, cationic impurities, and generated gases produced bythe electrosmosis and electrodialysis effect and existing within theprecipitated film is promoted, whereby effectiveness equal to orexceeding that of known applications such as repeated (secondary)painting and repeated electrodeposition is exhibited. Accordingly, theseparated quantity per unit of electrical power can besubstantiallyincreased to obtain an excellent coating film.

In the practice of the invention, moreover, by applying an externalmagnetic field on the anodic substrate on which the magnetic material isto be deposited and selecting the magnetic field direction so that aforce component which draws the magnetic particles toward the anode sideis created or so that the magnetic particles of the electrodepositedlayer are magnetically orientated as desired, it is possible to promotethe electrodeposition action or cause the electrodeposited magneticlayer to acquire magnetic axes as desired.

In this case, it is possible to impart the desired orientation in asmooth manner by further applying a deflecting magnetic field of adesired magnitude generated by an agency such as a current which varieswith time to the external magnetic field which contributes to theprincipal orientation of the magnetic spin and imparting a startingmoment to the magnetic spin. This method is, of course, similarlyeffective also in the succeeding drying step.

In the practice of this invention, the finer the magnetic particles tobe mixed into the electrolyte are, the more effective they are inincreasing the magnetisation unit number per unit volume of the finishedmagnetic layer, and an increase in the degree of filling of the magneticparticles in the magnetic layer causes an increase in the residualmagnetism.

Heret-ofore, in the application of a magnetic layer as a coating on asubstrate, the rapid evaporation of organic solvents has been consideredto be a great problem. The deposited film formed in accordance with thisinvention, however, does not contain an organic solvent. Moreover, thesolvent containing water as its principal constituent is separated outfrom this deposited film in the electrodeposition step, whereby thedeposited layer is a so-called solid component of a resin component andfiller in an unripened state.

Accordingly, in the drying step, the rate of thickness reduction issmall, as mentioned hereinbefore, and the fine and uniform dispersivityof the magnetic material is excellent. Therefore, a uniform recordinglayer of good homogeneity of the magnetisation characteristic within themagnetic layer and excellent recording resolution can be produced.

In the practice of the method of fabricating an electrodeposition layerof a magnetic recording medium, magnetic oxides such as 'y-Fe o Fe O CrOand ferrite or magnetic alloys of metals such as iron, nickel, andcobalt are used in the form of microgranular particles for the finemagnetic particles. For the electrolyte, a natural or synthetic,anionic, polyvalent polyelectrolyte having as its principal constituentat least one resin such as a watersoluble alkyd resin, a water-solublephenolic resin, or an acrylic resin is used.

For the substrate to be used in accordance with the invention forelectrodeposition thereon of the magnetic material, any material whichhas electroconductivity to function as the anode Within the electrolytecan be used. For example,'metallic conductors such as pure metals andmetal alloys, carbon, and semiconductors such as silicon and germaniumcan be used in any desired form.

However, in the case where a substrate material which readily forms anoxide film on its exposed surface, such as aluminium or chromium, or ametal which has been subjected to chemical surface processing is to beused as the anodic substrate, the surface of the substrate may becleaned beforehand by a mechanical or chemical process prior to theelectrodeposition step, Alternatively, the electrodeposition proceduremay be carried out with a high voltage such as to overcome theelectrical resistance of the oxide film.

It is possible, furthermore, to use poor conductors such as syntheticresins, cellulose acetate, and ceramics as the anodic substrate bycoating them with a metal thin film.

An electroconductive substrate is effective in preventing accumulationof electrostatic charge in mediums such as recording tapes. In thiscase, however, depending on the necessity the conductive film of thesubstrate to be coated with the magnetic mixture is oxidised in thesubsequent drying step or is heat teated in a manner such that finecracks are formed by a cause such as condensation of conductiveparticles thereby to transform the entire film into a non-conductivefilm, whereupon the recording tape thus fabricated can be caused to havecharacteristics equivalent to those of conventional magneticsoundrecording tapes in which electrically insulative substrates areused.

One example mode of practice of the invention is indicated in FIG. 1(A).'First, the example will be considered with the assumption that theinductance L, the capacitance C, and the A-C power supply shown in FIG.1(A) do not exist. Then, an emulsion electrolyte 1 prepared bydispersing microgranular magnetic powder in an aqueous solution havingan anionic, polyvalent polyelectrolyte as its principal constituent asdescribed hereinbefore is placed in an electrodeposition bath vessel 2,and an anode 3 and a cathode 4 are placed in opposed positions in theelectrolyte 1.

The anode 3 comprises an electrically insulative structure such as asynthetic resin or a ceramic and a coating on the surface thereof of ametal thin film deposited by evaporation deposition or some othersuitable process, whereby the surface is rendered conductive. Thecathode 4 is or ordinary type.

When a D-C current I from 'a D-C electric power source S is passedthrough the cathode 4 and the anode 3, a magnetic film is uniformly andfinely electrodeposited on the surface of the anode 3, whereby thisanode structure can be used as an excellent magnetic recording medium.

Next, an inductance L for cutting off alternating current, a capacitanceC for cutting off direct current, and an A-C power supply A areconnected as shown in FIG. 1(A), and electrodeposition is carried outefiiciently by superimposing an A-C bias current I on the aforementionedD-C current I whereupon a magnetic layer is deposited with even higheruniformity and fineness.

Circuits of further examples of apparatus which differ from that in FIG.1(A), and in which use is made of a superimposed current of a directcurrent and a current 6 varying with time, e.g., an alternating current,are illustrated in FIGS. 1(B) and 1(C), in which reference numerals andcharacters 1, 2, S, and A designate parts equivalent to those of thesame designations in FIG. 1(A).

The circuit shown in FIG. 1(B) is further provided with capacitors C forsuppressing direct current, coils L for suppressing the AC component,and rectifiers 14 for selectively determining the direction of passageof the D-C component. The circuit shown in FIG. 1(C) is provided with acapacitor C having the function of waveform smoothing, resistances orimpedances 16 and 17 for current adjustment, and rectifiers 15 forselectively determining the passage direction of the D-C component.

FIG. 1(A) illustrates an apparatus in which one anode and one cathodeare used, but the same effect can be obtained by dividing each of theseelectrodes into two or more divisional electrodes. Examples in each ofwhich two anodes 11 and 12 and a single cathode 13 are used are shown inFIGS. 1(B) and 1(C).

In order to indicate still more fully the nature and utility of theinvention, the following examples of specific practice embodying theinvention are set forth, it being understood that these examples arepresented as illustrative only and that they are not intended to limitthe scope of the invention.

Example 1 The apparatus illustrated in FIG. 1(B) was operated with anelectrolyte prepared by mixing fine particles of 'y-Fe O a magneticoxide, in a quantity of 15 percent by weight with a polyvalentpolyelectrolyte of a watersoluble alkyd resin containing 10 percent ofsolids. Flat and smooth metal sheets each measuring 10 x 50 mm. andhaving a thickness of 0.25 mm. were used for the anodes 11 and 12 andplaced in opposed positions spaced 40 mm. apart. The cathode 13 wasdisposed at a distance of 30 mm. from each of the anodes 11 and 12. Withthe above described apparatus and electrolyte and under the processconditions as set forth herebelow, the following results were obtained.

When electrodeposition was carried out by applying only a D-C voltage of30 volts until completion of the electrodeposition on the anodesurfaces, the layer thus deposited on each of the anodic substrates 11and 12 had a film thickness of 10 microns.

Then, when a D-C voltage of 20 volts and an A-C voltage of 10 volts weresimilarly applied, the resulting layers had a film thickness of 13.5microns. Furthermore, when a D-C voltage and an A-C voltage, each of 15volts, were applied, a finished film of a l5-micron film thickness wasobtained on each anode.

Thus, while each electrodeposition process is carried out with a totalapplied voltage of 30 volts, the electrodeposition efficiency in thecase of superimposition of DC and A-C voltages is higher than that inthe case where only a D-C voltage is applied. Moreover, by appropriatelyselecting the ratio of the A-C and D-C voltages, it is possible toproduce an excellent finished film.

Example 2 The circuit indicated in FIG. 1(C) was operated with anelectrodeposition bath vessel 2 provided with the same electrodeorganisation as that in example illustrated in FIG. 1(B) and with thesame electrolyte as that specified in Example 1, that is, an electrolyteprepared by mixing 15 percent by weight of fine particles of 'y-Fe Owith a polyvalent polyelectrolyte containing 10 percent of solids, thepH value of the electrolyte being approximately 7.

The operating conditions were as follows. A constant A-C voltage of 60lvolts was applied continually by the power supply A. Then, by causingresistance 16 to be amply high relative to resistance 17 and suitablyselecting the capacitance of capacitor C the ratio of the D-C componentto the A-C component applied to substrate 11 or 12 which functionsprincipally as the anode was caused to be 8:1, 4:1, 1:1, and 0.6:1, ateach of which ratios the process current was passed for 10 minutes.

Each film thus electrodeposited on the substrates 11 and 12 was washedwith water, dried, and heat treated to produce a finished film. Thefinished films thus produced with the above stated ratios hadthicknesses of 20, 22, 30, and 40 microns, respectively. When the sameapplied potential was supplied by bnly an A-C component to carry outelectrodeposition under conditions which were the same in all otherrespects as thoseset forth above, the thickness of the resulting filmwas only 11 microns.

As is apparent from the foregoing examples of practice, an appropriateselection of the D-C/A-C component ratio affords a remarkable increasein electrodeposition efiiciency per unit electrical quantity consumedrelative to that attainable through the use of only a D-C power supplyor an A-C power supply. Furthermore, in the case where there areadditives dispersed in a high-polymer electrolyte, not only can thedeposited coating quantity, i.e., the film thickness, be increased, butstructural features such as external appearance and texture of thefinished film can also be improved, and, moreover, higher adhesivity ofthe film with respect to the substrate and numerous other desirablefeatures relating to electrical characteristics are afforded.

The method of the invention as described above can be carried out toproduce various kinds of magnetic recording mediums, of which the mostimportant are in the form of rods or wires and strips, sheets, or tapesas described below with reference to FIGS. 2, 3, 4, and 5.

In one example of such a recording medium as illustrated in FIG. 2, thesubstrate 5 is in the form of an electroconductive rod or wirecompletely sheathed therearound by a recording medium layer 6 in which amagnetic oxide is admixed, and which has been electrodeposited on thesurface of the substrate 5 and dried. While this recording medium has anouter surface which is electrically insulative because of the highpolymer functioning as a binder therein, it is also possible, inaccordance with necessity, to apply a further protective coating layer 7of an electrically insulative material.

In another example of a magnetic recording medium' fabricated by themethod of the invention as illustrated in FIG. 3, at least one layer 8(two layers in the example illustrated) of an Fe-Ni alloy is depositedby a suitable method on the surface of a non-magnetic, electroconductivesubstrate rod or wire 5. Then, on the outer surface of the outermostlayer 8, a recording medium layer 6 having a magnetic oxide such as'y-Fe O as its principal constituent is electrodeposited.

In this organization, a combination of a magnetic alloy core wire and anon-magnetic metal coating therearound can also be used as the substratewire 5. In all cases, two or more composite laminations of magneticmaterials having respectively different magnetisation characteristicsare formed on and around the core wire 5. It is also possible tointerpose or sandwich a non-magnetic metal layer in an intermediateposition between these compound laminations.

The magnetisation characteristics of the composite magnetic laminationsare so arranged that, for example, the intermediate layer or layers havecharacteristics similar to those of permalloys which have relative lowvalues of coercive force H and a material of a magnetic characteristicwith a high coercive force H is utilised in the outermost layer. In thismanner, the magnetisation easy axes of the magnetic layers are allaligned beforehand in the same direction which is either in the Wireaxial direction or the wire circumferential direction or are orientatedin any desired angular direction. The coated wire thus produced can thenbe used as a wire memory constituting a non-destructive memory.(Reference: US. Ser. Nos. 471,589; 513,438; 515,310.)

The process of superposing a magnetic film of high coercive force in acomposite manner on another magnetic film by only a procedure such aselectroplating is accompanied in actualpractice by various difiicultiessuch as the necessity of high skill in adding a minute quantity ofcobalt. By the method of the present invention, however, this processcan be easily carried out. Furthermore, in this connection, an evengreater effectiveness in improv ing magnetic orientation characteristic,that is the squareness (or square-loop property) of the 3-Hcharacteristic curve of the finished electrodeposited layer can beattained by inscribing beforehand by a mechanical method fine scratcheson the surface of the substrate structure in the desired magnetisationdirection.

In the case of a conductive substrate structure in the form of a tape orsheet, fine particles of magnetic powder dispersed in a high-polymerresin can be electrodeposited as a magnetic recording material layer 6aon the surface on only one side of the substrate 5a as shown in FIG. 4.This may be accomplished by carrying out the electrodeposition with theother side (the side not coated) of the substrate covered by anelectrically insulative layer 9.

In this electrodeposition step, it is possible, of course, to impartdirectivity to the magnetic characteristic of the electrodepositedmaterial by causing the magnetic field due to the passage of the processcurrent or an external magnetic field to act directly on the substrate.It will also be obvious that, in the case of a recording medium of aspecific cross section, such as a wire or a tape, it is possible to forma closed magnetic circuit by electrodepositing a magnetic layer aroundthe entire outer surface of the substrate structure.

When narrow tapes are to be produced, the electrodeposition may becarried out on a wide sheet, which can then be cut into narrow strips ofthe required width.

Another example of a magnetic recording medium of sheet or tape formaccording to the invention, as illustrated in FIG. 5, is fabricated bycausing a metal thin film layer 10 to adhere by any suitable method tothe surface of an electrically insulative substrate 5a such as asynthetic resin or a ceramic and, with this metal layer 10 as the anode,electrodepositing on only this layer 10 a magnetic film 6a.

In the case where a large number of separate magnetic tracks are to beformed on an article such as a drum or a flat plate in theelectrodeposition of a magnetic recording material, theelectrodeposition may be carried out with insulative layers depositedbeforehand on the parts of the spaces between the magnetic tracks inaccordance with the principal described above with reference to FIG. 5.

Furthermore, the method of the present invention can, of course, beapplied to the fabrication of magnetic keepers in high-density memories.For example, electroconductive members in the form of wire or any otherdesired form may be provided beforehand between the bit storage pointsor between word storage parts, and then appropriate electrodeposition iscarried out with respect to these members. Alternatively, magneticlayers may be formed by the method of the invention in the proximity ofthe required points on the upper surface or lower surface of all bitstorage points forming the memory plane.

While the invention has been described above with respect to itsapplication to principally electrodeposition of magnetic coating layersof magnetic recording medlums, the invention is not limited to thissingle application. The method of the invention can be similarly appliedto accomplish effective electrodeposition of a wide range of coatinglayers containing fillers which have effects on electromagnetic,optical, and mechanical properties on materials or parts of variousarticles as, for example, automotive machines and equipment, electronicapparatus and devices, and components and parts thereof.

More specifically, examples of such fillers having effects onelectromagnetic, optical, and mechanical properties are fine particlesof such materials as electroconductors, magnetic materials,semiconductors, electrical insulators, dielectric materials, andluminous materials in photoelectric cells, photoconductive films, and ELluminescent materials. In particular, such luminous materials maycomprise zinc sulfide and fluorescent material mixed with metalparticles of, for example, aluminum and calcium. Fine particles of eachof these fillers, or a mixture of fillers for a combination ofcharacteristics, are dispersed in an aqueous solution having as itsprincipal constituent an anionic polyvalent polyelectrolyte to form anemulsion.

With this emulsion as an electrolyte and the substrate article as theanode, a current is passed through the electrodes in the same manner asdescribed herein above. This current is a direct current or a currentresulting from the superimposition on a direct current of a currentvarying with time, such as an alternating current, a pulse, or a pulsivecurrent. In this manner, a uniform and fine electrodeposited layer canbe produced on the substrate article by the same principle as in theproduction of magnetic recording mediums.

Various applications are obviously possible for the above mentionedlayers having combined characteristics. One example is a devicefabricated by electrodepositing in accordance with the method of theinvention a composite mixture layer of a dielectric material and amagnetic material on an electroconductive core wire. The dielectricmaterial comprises, for example, barium titanate or titanium oxide, andthe device including said composite mixture layer can be effectivelyutilised as a delay line element.

In the practice of this invention, the shape of the cathode is notlimited to that of a fiat plate 'but may be any suitable form such as anet or lattice, a grid, or one or more bars. Furthermore, the cathodematerial may be one which is generally used in processes such aselectrolysis and need not be limited to a specific material,

For the fine powder particles to be dispersed in the aqueous solution ofthe anionic, polyvalent polyelectrolyte, particles of any suitablematerial depending on the purpose of the electrodeposited layer can beused. For example, for electrodeposition coating of articles such asautomotive equipment, a material of the water-soluble alkyd resins classor a material of the acrylic resin class used for this purpose, that is,for coating metal surfaces, is amply suitable. Furthermore, theparticles to be added as a filler may also be a substance such as acolouring pigment generally used heretofore.

A further feature of this invention is that, in the practice thereof, itis also possible to move anodic substrate structures to be coated intoand out of the electrolytic bath successively in a continuous manner 'bymeans of roller driving devices, winding and unwinding devices, and thelike, or it is also possible to circulate the electrolyte. Furthermore,it is also possible, of course, to utilise the electrolytic bath vesselas the cathode.

I claim:

1. A method for producing magnetic recording mediums which comprises:preparing an electrolyte by dispersing fine magnetic particles, selectedfrom the group consisting of 'y-Fe O Fe O and CrO and ferrite ormagnetic alloys of metals such as iron, nickel and cobalt, in an aqueoussolution having as its principal constituent an anionic, polyvalentpolyelectrolyte consisting of a resin component; placing a cathode and asubstrate structure as an anode in said electrolyte; passing an electriccurrent through said anode and cathode to cause simultaneouselectrodeposition of a mixture of said particles and resin component asa coating layer on said substrate structure; and drying said coatinglayer to cause said resin component to undergo polycondensation andsolidification and to convert said resin component to a film providing abinder between said particles.

2. A method for producing magnetic recording mediums which comprises:preparing an electrolyte by dispersing fine magnetic particles, selectedfrom the group consisting of 'y-Fe O Fe 0 and CrO and ferrite ormagnetic alloys of metals such as iron, nickel and cobalt, in an aqueoussolution having as its principal constituent an anionic, polyvalentpolyelectrolyte consisting of a resin component; placing a cathode and asubstrate structure as an anode in said electrolyte; simultaneouslypassing an electric current through said anode and cathode andsubjecting said anode to an external magnetic field to causesimultaneous electrodeposition of an electrically insulative mixture ofsaid particles and resin component as a coating layer on said substratestructure; and drying said coating layer to cause said resin componentto undergo polycondensation and solidification and to convert said resincomponent to a film providing a binder between the fine magneticparticles.

3. A method for producing magnetic recording mediums as claimed in claim2 in which said external magnetic field is applied in the direction inwhich the fine magnetic particles within the electrolyte are attractedto the anode.

4. A method for producing magnetic recording mediums as claimed in claim2 in which said external magnetic field is applied in a direction suchthat a magnetic orientation in a specific direction is imparted to themagnetic particles within said coating layer.

5. A method for producing magnetic recording mediums as claimed in claim2 in which said electric current passed through the anode and cathode isapplied as a direct current.

6. A method for producing magnetic recording mediums as claimed in claim2 in which said electric current passed through the anode and cathode isapplied as a combined current consisting of a direct current and acurrent which varies with time and is superimposed on said directcurrent.

7. A method for producing recording mediums as claimed in claim 2 inwhich said external magnetic field is applied to impart a starting forcecomponent to the magnetic spin thereby to facilitate deflection.

8. A method for producing magnetic recording mediums as claimed in claim4 in which a second magnetic field is applied during said drying step toimpart a starting force component to the magnetic spin to facilitatedefiection.

9. A method for producing magnetic recording mediums as claimed in claim2, comprising the step of preparing said substrate structure byelectrodeposition of a conductive coating of a metal thin film on asubstrate material selected from the group consisting of syntheticresins, cellulose acetate, and ceramics, and performing said drying stepafter said deposition of said coating layer to form oxidation only onsaid conductive coating to convert said conductive coating to anon-conductive coat- 10. A method for producing magnetic recordingmediums as claimed in claim 2, comprising the step of preparing saidsubstrate structure by electrodeposition of a conductive coating of ametal thin film on a substrate material selected from the groupconsisting of synthetic resins, cellulose acetate, and ceramics, andperforming said drying step after said deposition of said coating layerto form cracks only on said conductive coating to convert saidconductive coating to a non-conductive coat- 11. A method for producingmagnetic recording mediums as claimed in claim 2, in which saidsubstrate structure comprises a non-magnetic electroconductive substratehaving an Fe-Ni alloy deposited thereon.

12. A method for producing magnetic recording mediums as claimed inclaim 11, in which said Fe-Ni alloy has a coating of a non-magneticmetal layer.

(References on following page) 12 References Cited 3,362,899 1/1968Gilchrist 204181 UNITED STATES PATENTS 3,525,679 8/1970 WilCOX 61; 3.1.204181 6/1947 Robinson et al. 204-1s1 X DANIEL -WYMAN, Primary Examiner3/1956 McBride 204-181 X 5 W. J. SHINE, Assistant Examiner 11/1959Satriana et a1. 204-181 Us. cl X.R- 10/1967 Matkan et a1. 204-181 117235 240

